Creating a 3D Spline

Select a visualization plane.

Select the check boxes to perform the corresponding actions.

Edit Mode, switches to edition, provided at least two points have been created.
Tip: Selecting a 3D Spline before launching the command starts the edit mode.
Close feature
Point on support to create points on geometries.
Update when dragging points
Project spline on a support, provided all the points of the spline are on the same support.
Extrapolate spline, to extrapolate the spline to intersect the sides of the support surface. The spline is smoothed for a better quality.
The spline must be projected on the support surface (Volumes or solids are not supported).

Alternatively, from the 3D area

Creates a projected point on the feature under the cursor
Creates a projected point on the feature under the cursor, that has the same coordinates than the snapped point.
Creates a projected point on the feature under the cursor that has a coordinate on the edge.
Creates a point in the 3D area. The grid is an information of the location of the point.
Adds points on the spline.
Snaps the point on the spline.

In edition mode, use the context menu to.